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Tuesday, October 12, 2010

Scientists have been able to trace the annual journeys of individual Red Knots using tracking devices attached to the birds' legs. (I linked to an article on this in my last Loose Feathers edition, but I think it deserves its own post so that it does not get lost among the other articles.) Prior to this study using geolocators, the general outline of the birds' migration was already known: most Red Knots winter in Tierra del Fuego, make migratory stopovers along the Atlantic coast (especially Delaware Bay), and breed in Arctic Canada.

The geolocator study added some detail to the general picture and emphasized just how important horseshoe crabs are for Red Knots' survival. The bird whose data is presented in the graphic at right (click to see a larger version) made several nonstop long-distance flights, including one over 2,000 miles, another over 3,000 miles, and a third of almost 5,000 miles. The last of those flights crossed the Amazon, the Caribbean, and part of the Atlantic before it terminated in Ocracoke, North Carolina, right around the time that horseshoe crabs would be spawning. At that point, the bird would be tired, starving, and in need of some quick nutrition in the form of fresh horseshoe crab eggs.

The study was funded by the U.S. Bureau of Ocean Energy Management, Regulation and Enforcement, which wanted better data on how offshore wind energy projects might affect Red Knots, Piping Plovers, and Roseate Terns – three vulnerable species that migrate or breed along the U.S. Atlantic coast. Several wind farms are already planned in the vicinity of Delaware Bay.

Here is a bit more about the technology behind the study:

Basically, the geolocators determine location by measuring daylight. The length of a day shows the bird's latitude, and the time of local "noon" - when the sun is at its highest - shows longitude....

Far better devices exist than even the geolocators, but only for larger birds. Several years ago, Pennsylvania officials outfitted a peregrine falcon with a solar-powered backpack that transmitted fixed GPS locations to a land-based receiver - allowing scientists to fly along virtually via a laptop.

The geolocators were developed by the British Antarctic Survey in England. Every year, they are able to tweak the technology to get a smaller instrument, said James Fox, an electronics engineer with the Survey.

The problem is that the devices for the red knots need to be so small that it's impossible to add the capability to transmit. To get the data, the scientists have to find the birds and recapture them.

The scientists capture and tag the birds at Delaware Bay since so many Red Knots gather there during the spring and then recapture them at the same site the following year. So far 47 Red Knots have been tagged with geolocators and three have been recaptured. When (if?) the other birds are recaptured, there will probably be more interesting tales in the data.